Roofing systems are well known in which a roof deck supports thereon a plurality of layers of materials for forming a finished waterproof roof surface over an enclosed space. In commercial structures and other relatively flat roof structures, various materials are known and used in combinations thereon for building up a finished roof on such structures as specified in the trade. Generally the roof deck supports an insulation layer of fiberboard or the like which provides a rigid, continuous, flat, upper surface on which a roof convering is applied. One of the well known forms of building up a roof covering is to mop on hot asphalt and apply roofing "felt" in multiple layers to provide the necessary strengths and impermeability to rain water required for a satisfactory roof.
Conventional built-up roofs have a number of shortcomings. The application of three or more layers of roofing felt by mopping on with hot asphalt is a time consuming and labor intensive task which adds considerable expense to the finished structure. The roofing felt is a relatively brittle material which cannot be unrolled from the roll when the roll is cold and hence operation in cold weather or repairs during emergencies in cold weather are difficult. Furthermore, the multiple layers of roofing felt plus the mopped on asphalt amounts to a large mass of inflammable molten material in the event of a fire which would heat the roof to the point of pooling and dripping of free asphalt from the composite layers to further feed the fire within the building. Furthermore, such a roof is fragile with respect to impact strength and thus can be damaged by hail. Such roofs also have poor lateral flexibility so the ordinary expansion and contraction due to ambient temperature changes will, over a period of time, result in cracking and allow water leakage. Similar problems occur when workmen walk on such a roof and cause some degree of deflection of the supporting structure.
An additional expense in installing such a roof is involved with extending the roof felt layers through a right angle corner. The standard practice is to install a wooden cant in the form of a rip sawed square timber to fit in the corner before the roofing layers are applied so that the right angle bend is traversed through two successive forty-five degree angle bends. In addition, at the usual places on a roof, separate flashing materials are required because of the limited capability of roofing felt to bend around corners or be durable enough to survive in valleys between gable surfaces and the like.
Alternate forms of roof covering include elastomeric compounds in the form of thin membranes such as the Sure-Seal (.TM.) material sold by Carlisle Tire & Rubber Co. as a roof covering. Both the standard asphalt felt as well as rubber and other composite membrane roof converings are described, for example, in the 1980 Factory Mutual Approval Guide for building materials and construction, pp 442-461. Rubberized roof and gutter coverings are generally required to be covered with loose stone or otherwise protected from oxidation and deterioration from the ultraviolet exposure to sunlight and to avoid abrasion or puncturing where the roof has occasional maintenance traffic of workers thereon.